Early development in virtually all animals is characterized by the formation of three primary germ layers, which significantly limits the developmental fate of the cells. In some cancers, developmental controls limiting cell fate are often not present, or are misregulated, leading to cellular proliferation rather than differentiation. The Rothman lab studies how cell fate is limited, and has recently identified a GATA family transcription factor, end-1, as a key determinant in limiting cells to an endoderm fate in the nematode, C. elegans. End-1 is the first zygote gene shown to specify the fate of a founder cell (E), a germ layer (endoderm and an organ (the gut). The experiments outlined in this proposal use genetics to determine how end-1 specifies endoderm by isolating a specific null allele of end-1, and performing a screen to identify directly interacting genes, and genes in the same pathway. Cell lineage analysis, laser ablation, mRNA and protein localization will be used to characterize the mutants. In addition, genes that end-1 transcriptionally regulates will be identified from a C. elegans library in yeast, and characterized using molecular biology techniques. By identifying the key proteins that interact with end-1 as well as key proteins that are regulated by end-1, the proposed experiments will begin dissect the molecular pathway of endoderm specification.